1. Field of the Invention
The present invention relates to an oscillating actuator, and more particularly to an oscillating actuator for disk apparatuses such as a hard disk or magnetic disk apparatus which exhibits excellent dimensional stability and can be produced easily and economically.
2. Description of Related Art
Actuators heretofore used for disk apparatuses generally comprise, as shown in FIG. 8, a carriage member 2 having a multi-layer structure having a plurality of arms 5 and a movable coil 3 which is held by a coil-holding member 1 and oscillates the carriage member around a bearing hole 4. A head suspension in which a functional member such as a magnetic head (a magnetic sensor) or the like is disposed is to be attached to the tip portion of each arm. The movable coil is a coil prepared by winding an electrically conductive wire coated with an electrically insulating film. When an electric current is passed through the coil, driving force works on the coil by the effect of a magnetic circuit having a permanent magnet (not shown in the figure) and the carriage member oscillates around the bearing hole.
Heretofore, the carriage member is made of a metal material such as an aluminum alloy from the standpoint of strength and workability. However, production of the carriage member made of a metal material such as an aluminum alloy requires many working steps for shaping and cutting. Therefore, the production cost is high and productivity is poor.
Recently, due to the requirement for increasing the recording density of magnetic disks and decreasing the access time, lighter oscillating actuators are desired to further improve precision and speed of positioning of oscillating actuators. Thus, oscillating actuators having arms made of a resin have been developed.
For example, in Japanese Patent Application Laid-Open No. Heisei 8(1996)-306141, as the arm made of a resin which can be produced at a low cost and shows excellent dimensional stability and mechanical properties, an arm which has a metal member having a penetrating hole for attaching a head suspension at the tip portion and formed from a thermoplastic resin integrally in combination with the metal part in accordance with injection molding has been proposed. However, the arm having the member made of a resin has a problem in that deformation such as camber tends to take place due to difference in the rate of solidification between surface portions and inner portions.
In Japanese Patent Application Laid-Open No. Heisei 8(1996)-336854, as the process for producing an arm having excellent dimensional stability using a resin at a smaller cost, a process is proposed in which an intermediate product having a connecting portion made of a resin, which is to be cut off or removed, between arm parts is prepared in accordance with injection molding and the connecting portion made of a resin is cut off from the prepared intermediate product after the intermediate product has been solidified sufficiently. However, in accordance with this process, it takes a longer time for the production due to the necessity for removing the connecting portion made of a resin and this process is disadvantageous with respect to productivity. Moreover, it is difficult to produce a carriage having a precision sufficient for precision instruments such as disk apparatuses.
An object of the present invention is to provide an oscillating actuator for disk apparatuses such as a hard disk or magnetic disk apparatus which exhibits excellent dimensional stability and can be produced easily and economically.
As the result of intensive studies by the present inventors to overcome the above problems, it was found that deformation (camber) of an arm during production of a carriage member can be prevented when an arm of a carriage member has an intermediate portion and a head portion arranged in this order from a bearing hole in the carriage member and the intermediate portion has a thickness smaller than a thickness of the head portion and dimensional stability of the product can be improved. The present invention has been completed based on this knowledge.
The present invention provides:
(1) An oscillating actuator which includes a coil-holding member and a carriage member including a bearing hole and one or more arms, wherein the arm has an intermediate portion and a head portion arranged in this order from the bearing hole in the carriage member and the intermediate portion has a thickness smaller than a thickness of the head portion;
(2) An oscillating actuator described in (1), wherein the carriage member is integrally formed from an electrically conductive resin;
(3) An oscillating actuator described in (1), wherein the carriage member is a laminate in which arm pieces and spacers are alternately disposed and are made of an electrically conductive resin;
(4) An oscillating actuator described in (1), wherein the arm has a plurality of protrusions which are disposed on side faces of the arm alternately at upper and lower positions and used for containing lead wires;
(5) An oscillating actuator described in (1), wherein grooves extending from the head portion toward the bearing hole are formed on a face of the arm;
(6) An oscillating actuator described in (1), wherein ribs extending from the head portion toward the bearing hole are formed on a face of the arm; and
(7) An oscillating actuator described in (6), wherein second ribs are formed on a face of the arm in a direction perpendicular to the ribs extending from the head portion toward the bearing hole.
Preferable embodiments of the present invention include:
(8) An oscillating actuator described in (1), wherein the arm has a base portion at a position close to the bearing hole in the carriage member and the base portion has a thickness greater than a thickness of the intermediate portion;
(9) An oscillating actuator described in (1), wherein the thickness of the intermediate portion is about 50 to about 80% of the thickness of the head portion;
(10) An oscillating actuator described in any of (2) and (3), wherein the electrically conductive resin includes a thermoplastic resin and carbon fiber; and
(11) An oscillating actuator described in (10), wherein the content of the carbon fiber is about 10 to about 100 parts by weight based on 100 parts by weight of the thermoplastic resin.